Units of Measurement

Measurement is used to measure quantities.

Quantity is something that has magnitude, size, or amount (volume).

A quantity is not the same as a measurement.

In the late 18th century, scientists used the metric system. The metric system is a forerunner to the SI System.

Scientists all over the world use a single measurement system called Le Systeme International d’Units, abbreviated SI.

It was adopted in 1960 and has both base units and derived units.

The most common base units that we will study include:

QuantityQuantity Symbol

Unit nameUnit

abbreviation

Length l meter m

Mass m kilogram kg

Time t second s

Temperature

T Kelvin K

The SI standard unit for length is the meter. A distance of 1m is about the width of an

average doorway. To express longer distances, the kilometer

(km) is used. One kilometer is equal to 1000 m.

To express shorter distances, the centimeter (cm) is used. One centimeter is equal to 1/100 of a meter.

Length can be measured using a meter stick or rulers.

Mass is a measure of the quantity of matter. The standard unit for mass is the kilogram (kg).

The gram (g), which is 1/1000 of a kg is used for measuring masses of small objects such as flasks and beakers. Mass is typically measured using a balance.

Mass is different from weight. Weight is a measure of the gravitational pull on matter. The weight of an object increases as gravity acts on it. The weight of an object on the moon is about 1/6th of its weight on Earth. So, a human on Earth who weighed 126 lbs. would weight how much on the moon?

The standard unit of measurement for time is the second (s).

Time can be measured using stop watches, clocks, count down timers, and other time pieces.

Larger amounts of time are measured in minutes and hours.

There are 60 seconds in one minute. There are 60 minutes in one hour. Given that there are 24 hours in one day, how many seconds are there in one day?

The standard unit of measurement for temperature is degrees Kelvin (K).

Temperature can also be measured in degrees Celsius (°C) and degrees Fahrenheit (°F).

To convert degrees Celsius (°C) to degrees Fahrenheit (°F) multiply by 1.8 and then add 32. To convert degrees Fahrenheit to degrees Celsius, subtract 32 and then divide by 1.8

° K= °C + 273 Temperature is measured using a

thermometer. (measures the degree of heat or coolness)

Derived units are combinations of base units. They are produced by multiplying or dividing standard units. The derived units we will study include:

QuantityQuantity symbol

UnitUnit abbreviation

Area Asquare meter

m2

Volume Vcubic meter

m3

Density Dkilograms per cubic meter

kg/m3

Volume is the amount of space occupied by an object. The derived SI unit for volume is cubic meters. The cubic meter is rather large, so a more common unit of cubic centimeters is more commonly used.

Non-SI units are also used to measure volume such as the milliliter (mL) and the liter (L), which is 1000 cm3. There are 1000 mL in 1 L.

Beakers, flasks, and graduated cylinders are often used to determine the volume of liquids.

Density is the ratio of mass to volume, or mass divided by volume. It can be written:

density=mass/volume or D=m/V Density is a characteristic physical

property of a substance that does not depend on the size of the sample. As the mass of an object increases, its volume increases.

* Question: Are raisins, more or less dense than soda water? Let’s see!

Name Volume (cm^3) Mass (kg)

Michael 120384 85

John 77509 59Colleen 35000 56

Fabrizio 135456 80Abella 47824 62

Aaron 174096 101

Felicita 95700 63

Travis 89775 102

Franklin 97559 70

Steven 90580 70

Kayla 90180 65

Nicholas 89280 66Brianna 100200 70

Name Volume = “X” Mass = “Y”

Oscar 109620 cm^3 74kg 0.000235

Crystal 69,900 cm^3 51kg 0.0002857

Ron 172,900 cm^3 79kg 0.000222

Brian 170280 cm^3 74kg 0.0002

Chevon 126412 cm^3 65kg 0.000211

Amber 94350 cm^3 0.0002

Maria 56160cm^3 49kg 0.0002

Danielle 115520 cm^3

Robert 131760cm^3 60kg 0.00021

Emmanuel 129960 cm^3 62kg 0.000192

Brittany 95456 cm^3 55kg 0.00027

Alyssa 110160 cm^3 0.00027

Jaclynne 65490 cm^3 50kg 0.0003

Jake 142740 cm^3 67kg 0.0003